Fiber optic waveguides are fibers of glass or of synthetic plastic material typically having a very small diameter on the order of 0.1 to 0.01 mm. A typical fiber optic waveguide comprises a core of glass and a sheath or cladding layer, wherein the index of refraction of the cladding layer is smaller than that of the core. The index of refraction of the core may be constant, or it may vary radially according to a predetermined formula, thereby creating a graded index fiber optic.
Owing to this difference in the index of refraction between the materials constituting the core and the cladding layer, light, entering one end of the fiber, is transmitted along the axis of the fiber within the core. By employing particular types of highly transparent glass, it has been possible to transmit the light from one end of the fiber to the other with very little attenuation or dispersion.
Nevertheless, physical constraints on the behavior of light have prevented the use of fiber optic waveguides in certain applications, notably any application in which the light must be directed at an obtuse angle relative to the optical axis of the fiber over a very short distance. In this case, tightly bending the fiber optic is an inadequate means in that the fiber becomes fatigued and will break or the light will be lost due to radiation at the sharp bend.
In such a circumstance, it has been proposed to utilize mirrors and highly polished optics to reflect the light at the needed angle. In doing so, an apparatus can be designed with convex, concave, or flat optical components for reflecting the incident light. However, while the proposed solutions accomplish some of the stated goals, they do so at an increased cost and with little regard for the overall efficiency and constraints on the bulkiness of the optics
Accordingly, the present invention includes a fiber optic waveguide that consists of a cladding layer that surrounds the core, which guides and directs a beam of light. The cladding layer defines a first boundary and a focusing end, where focusing end of the fiber optic waveguide defines a reflecting surface. From the reflecting surface, a surface normal vector is projected for determining the relative position of the surface to the optical axis. The focusing end is polished at an angle such that the surface normal does not coincide with the optical axis, which is defined by the path of the beam of light through the fiber optic waveguide. The angle θ is necessarily greater than 0 degrees and less than 90 degrees. In particular embodiments, the angle θ is between 36 and 55 degrees, and, for particular applications, may be approximately 43 to 49 degrees.
The present invention further includes a focusing lens coupled to the outer surface of the cladding layer of the fiber optic waveguide at its focusing end. The focusing lens may be a ball lens, and it is attached to the exterior of the cladding layer by an adhesive material, preferably of an index-matching type. As such, upon reflection from the focusing end, the beam of light is transmitted through the index-matching adhesive material and through the attached focusing lens to a second boundary, which is the outer surface of the focusing lens. As the focusing lens is spherical in nature, the second boundary appears as a spherical lens to the beam of light. Therefore, the beam of light converges into an circular spot, which is on the order of 5–9 μm in diameter.